Disodium 3-amino-1-hydroxypropane-1,1-diphosphonate or "disodium pamidronate" has the formula: ##STR1##
It is commercially available as the lyophilized pentahydrate, under the name AREDIA.RTM. from Novartis Pharmaceuticals Corp., and is used to inhibit bone resorption, i.e., to treat moderate or severe hypercalcemia associated with malignancy, with or without bone metastases. The preparation of the crystalline pentahydrate from pamidronic acid is disclosed by Stahl et al. in U.S. Pat. Nos. 4,711,880 and 4,639,338. This material is prepared by partially neutralizing a heated slurry of pamidronic acid with aqueous sodium hydroxide (NaOH) to pH 7-7.5 and then initiating crystallization at .gtoreq.50.degree. C. The mixture is slowly cooled to 0-5.degree. C. and the disodium pamidronate is collected by filtration. This product is described as having "excellent crystallinity" and as being "completely stable to storage under approximately normal ambient conditions." It comprises about 24.1-25% water.
The crystalline product ("Modification E") is contrasted with an amorphous product disclosed to be prepared by the general process of Jary et al. (U.S. Pat. No. 4,304,734). In Comparison Example 1 of the '338 patent, pamidronic acid is neutralized to pH 7.4 with aqueous NaOH and the reaction mixture is concentrated to dryness under reduced pressure at 60-70.degree. C. and then dried at 20 mbar to constant weight. However, the amorphous product that is obtained is described as deliquescent in air, contains 12.9% of retained water and, as taught in the '338 patent, will convert to the pentahydrate. Stahl et al. also teach the interconversion of other crystalline forms of disodium pamidronate depending upon humidity and amount of water present, which demonstrates the difficulty in utilizing preformed disodium salts of pamidronic acid for further processing into sterile pharmaceutical dosage forms.
Thus, a need exists for a simple method to prepare disodium pamidronate that is stable to storage and suitable for reconstitution and intravenous infusion/injection.